The present invention relates to a method and an apparatus for estimating a camera motion; and, more particularly, to a method and an apparatus for estimating a camera motion, in which the motion of a camera made at the time of photographing can be extracted from a moving picture photographed by the camera to be used for moving picture classification and search.
PCT Appln. No. WO 00/42771 discloses xe2x80x9cCamera Motion Parameters Estimation Methodxe2x80x9d.
The disclosed camera motion estimation method includes the steps of extracting from a video sequence vectors corresponding to the motion between two successive frames, the motion vectors forming the camera velocity field; preprocessing the camera velocity field so as to reduce the amount of data and the heterogeneousness of the extracted motion vectors; estimating for each pair of frames, from the preprocessed field, camera features between the two considered frames; and undertaking a long term motion analysis based on the estimation in order to obtain motion descriptors corresponding to the estimated camera motion parameters.
The camera motion estimation method constructed as described above is applied to a sequence of successive video frames divided into blocks, and can be employed to implement descriptors within Moving Picture Experts Group (MPEG) 7.
In the estimation method, the extraction of the motion vector is carried out using block matching motion compensation, which is employed as a part of the predictive coding process widely used in video transmission for reducing the amount of information needed to encode a video sequence. To be specific, each frame is divided into a fixed number of blocks, and for each block, a search is made for the most similar block in a previous reference frame, over a predetermined area. The search criterion is generally the search of the best matching block, giving the least prediction error. A motion vector is computed on the basis of the positions of each pair of similar blocks, and a camera parameter between each pair of frames is computed using the computed motion vector and a certain camera motion equation.
As described above, in the conventional camera motion parameter estimation method, a motion vector is extracted by comparing a reference frame with a current frame and a camera motion parameter is estimated using the motion vector. However, the conventional camera motion parameter estimation method has drawbacks in that the speed of parameter estimation is not desirable.
Accordingly, the development of a camera motion parameter estimation method or a camera motion estimation apparatus, which is capable of increasing the speed of estimation, is highly desired.
It is, therefore, an object of the present invention to provide an apparatus for estimating a camera motion, in which horizontal and vertical mean pictures are generated with respect to each of the blocks of each picture frame throughout the entire picture frames and motion vectors are extracted from the horizontal and vertical mean pictures, thereby increasing the speed of camera motion estimation.
Another object of the present invention is to provide a method for estimating a camera motion, in which a picture frame is divided into a plurality of blocks, horizontal and vertical mean pictures are generated with respect to each block, motion vectors are extracted from the horizontal and vertical mean pictures, and then the camera motion is estimated by the combination of the motion vectors.
In accordance with an aspect of the present invention, there is provided a camera motion estimation apparatus for extracting a camera motion made at the time of photographing from a photographed moving picture, comprising: a frame picture memory unit for storing a plurality of moving picture frames with one frame separated from another; a buffer for sequentially extracting the frames stored in the frame picture memory unit and storing them; a block division unit for dividing each of the frames stored in the buffer into a plurality of blocks; a mean picture generation unit for generating horizontal and vertical mean pictures using the blocks obtained through the block division unit to estimate a camera motion; a horizontal and a vertical mean picture memory unit for storing the data of the horizontal and the vertical mean pictures generated in the mean picture generation unit; a motion vector extraction unit for extracting motion vectors from the blocks using horizontal and vertical mean picture data stored in the horizontal and the vertical mean picture memory unit; a motion vector memory unit for storing the data of the motion vectors extracted in the motion vector extraction unit; and a camera motion estimation unit for estimating a camera motion using the motion vector data stored in the motion vector memory unit.
In accordance with another aspect of the present invention, there is provided a camera motion estimation method of extracting a camera motion made at the time of photographing from a photographed moving picture, comprising the steps of: dividing each of successive frames into a plurality of blocks and generating horizontal and vertical mean pictures with respect to each of the blocks; extracting a representative motion vector with respect to each of the blocks using the horizontal and the vertical mean pictures; estimating a partial camera motion within each of the blocks using the representative motion vector; and estimating the entire camera motion within the moving picture on the basis of the partial camera motions.